Ultra low frequency electromagnetic wave anomaly and its spectrum characteristics before earthquakes |
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Authors: | Jian-Guo Hao Yun-Fu Zhang Huai-Wen Pan De-Rui Li Tian-Ming Tang and Xiao-Qin Liu |
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Institution: | (1) Institute of Geophysics, State Seismological Bureau, 100081 Beijing, China;(2) Oil and Natural Gas General Company of China, 100724 Beijing, China;(3) Department of Scientific Programming and Earthquake Monitoring, State Seismological Bureau, 100036 Beijing, China |
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Abstract: | Many observations and researches show that abundant and intense ultra low frequency (ULF) electromagnetic anomalies appeare
before local earthquakes. In order to understand this phenomenon systematically, the transmission property and the formation
of the seismic-electric dipole are discussed in this paper. The results show that the vertical component of the ULF electric
anomaly before earthquake has the properties of better penetration, less disturbance and high signal-to-noise ratio. The signal
can be easily extracted and received. The anomaly should be an important way to seek for reliable short-term and imminent
earthquake precursors. After the spectrum analysis of the (ULF) electric field anomalies, we found that the periods of the
anomaly related to local earthquakes are from a few minutes to a dozens minutes. There is a relation between the spectrum
of the anomaly and the epicentral distance. The ULF electric field anomalies strongly rely on the orientation of the seismogenic
zone. The percolation electric field anomaly and its spectrum amplitude do not have obvious relation with the size of local
earthquakes.
Contribution No. 94A0097, Institute of Geophysics, SSB, China.
The English version is improved by Prof. Guo-Hua FAN, Institute of Geophysics, State Seismological Bureau. |
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Keywords: | earthquake precursor frequency spectrum electromagnetic method atmospheric electric field |
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